Without limiting the scope of the present invention, its background is described with reference to chemical injection into a wellbore that traverses a hydrocarbon bearing subterranean formation, as an example.
It is well known in the subterranean well production art that wellbore chemical management can be important in optimizing fluid production as well as in minimizing well downtime and expensive intervention. For example, applications of chemical injection systems include scale, asphaltines, emulsions, hydrates, defoaming, paraffin, scavengers, corrosion, demulsifiers and the like. In a typically installation, the chemical injection system includes a chemical injection mandrel interconnected in the tubing string and having an injection port positioned at the desired injection location. One or more chemicals are supplied to the chemical injection mandrel via a chemical injection line that extends to the surface and is coupled to a chemical injection pumping unit. Various control and communication lines may also extend between the chemical injection mandrel and the surface control equipment. The chemical injection mandrel generally includes a check valve positioned between the chemical injection line and the injection port. The purpose of the check valve is to prevent wellbore fluids, such as production gas, oil or water, from migrating into the chemical injection system upstream of the check valve.
It has been found, however, that during the production life of the well as the bottom hole pressure depletes, the higher density of the chemical injection fluid compared with the production fluids generates a high hydrostatic differential, which forces the fluid level in the chemical injection line to be balanced with the bottom hole pressure at the injection point any time chemical injection is interrupted. For example, in certain installations, such deep water installations or multipoint chemical injection installations, if the bottom hole pressure gets equalized at the chemical injection point, the well fluids will try to migrate through the check valve into the chemical injection line, resulting in a risk to generate hydrates at the subsea level. In these installations, even the option of closing a surface control valve could generate a vacuum in the chemical injection line resulting in a risk of precipitate solids building up in the injection line, which can plug the injection line.
Therefore, a need has arisen for an improved chemical injection system operable for optimizing wellbore chemical management and fluid production. A need has also arisen for such an improved chemical injection system that is operable for deep water, depleted well and/or multipoint chemical injection installations. Further, a need has arisen for such an improved chemical injection system that is operable to prevent production fluid migration into the injection line.